To solve the problem of voltage rise in a clamp capacitor in active clamp circuits.

A switch module includes: a first series circuit in which a switch Q1, a switch Q2, and a diode D1 are connected in series in this order between a first terminal and a second terminal; a second series circuit in which a diode D2, a switch Q3, and a switch Q4 are connected in series in this order between a third terminal and a fourth terminal; a fifth terminal connected to the point of junction between the switch Q1 and the switch Q2; a sixth terminal connected to the point of junction between the switch Q2 and the diode D1; a seventh terminal connected to the point of junction between the diode D2 and the switch Q3; and an eighth terminal connected to the point of junction between the switch Q3 and the switch Q4. A resonant capacitor C1 is connected between the sixth terminal and the seventh terminal and a resonance reactor L1 is connected between the fifth terminal and the eighth terminal so as to form a series resonance of the resonant capacitor C1 and the resonance reactor L1. The voltage of the resonant capacitor C1 is thereby clamped to a supply voltage.